Iodine-containing electric incandescent lamp with heat conserving envelope



Sept. 28, 1965 G. A. FREEMAN 3,209,188

IODINE-CONTAINING ELECTRIC INCANDESCENT LAMP WITH HEAT CONSERVINGENVELOPE Filed Feb. 21. 1961 FIG. I.

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INV EN TOR. 650/?65 /7. FREEMfl V.

S :E (ME United States Patent IUDllNE-CONTAINING ELECTRIC INCANDES- CENTLAMP WITH HEAT CQNSERVING ENVELOPE George A. Freeman, East Orange, N.I.,assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Filed Feb. 21, 1261, Ser. No. 90,804 16Claims. (Cl. 3134'3) This invention relates in general to electric lampsand, more particularly, to an improved electric incandescent lamp forgeneral lighting service.

Recently there has been developed and marketed a very compact highefficiency electric incandescent lamp having a tungsten filament whereinthe undesirable erosion of the filament by progressive vaporization andthe resultant bulb blackening during life are minimized by means ofiodine vapor that is sealed within the lamp. The wattage rating of thefilament and the dimensions and configuration of the bulb are socorrelated that the normal operating temperature of the inside surfaceof the bulb walls is within the range of about 250 to 1200 C. At thistemperature the iodine vapor combines chemically with vaporized tungstenparticles deposited on the bulb surfaces and starts a regenerativegettering cycle that redeposits the vaporized tungsten back onto thefilament. The progressive deterioration of the filament and attendantblackening of the bulb by vaporized tungsten are, accordingly, reducedto a minimum resulting in a marked increase in both the lumenmaintenance and useful life of the lamp.

In order to meet the critical bulb wall temperature either very highwattages or very small bulb sizes have heretofore been required. Forexample, tubular 500 watt 120 volt lamps of this type now being marketedhave a length of about 4 /2" and an outside diameter of about A 100 watt28 volt lamp of ellipsoidal configuration, on the other hand, would havea major diameter of about 7 and a minor diameter of about High wattagecompact lamps of this type and the manner in which the iodine vaporcoacts with the vaporized tungsten and the filament to elfect thedesired regenerative gettering cycle are described in detail in US.Patent No. 2,883,- 571 issued April 21, 1959, to E. G. Fridrich et al.

The small bulb sizes presently required in order to obtain the high bulbwall temperature necessary for the desired iodine-tungsten reaction hasprevented the use of such lamps for general lighting purposes becausethe lamp dimensions and shapes are unsuitable for existing fixtures andsockets. In addition, the base temperature of such lamps exceed by .alarge margin the safe temperature limits established for sockets of thetype employed in general lighting fixtures.

It is accordingly the general object of this invention to provide aniodine-containing electric incandescent lamp that exhibits the improvedperformance of such lamps and permits the use of more suitable bulbshapes and sizes for a given wattage rating.

Another and more specific object is the provision of a high-efficiencyiodine-containing electric incandescent lamp that can be made in avariety of wattages and sizes and which can be safely operated inexisting general lighting fixtures and sockets.

The aforesaid objects, and others which will become apparent as thedescription proceeds, are achieved by providing a heat conserving meanson the envelope which raises the wall temperature thereof to thecritical temperature required for the iodine-tungsten reaction but whichotherwise would not be attained either because of the size orconfiguration of the envelope. Specifically,

a thin coating of tin oxide or the like, such as the socalled EC coatingmarketed by the Corning Glass Works, which reflects infrared radiationsbut transmits visible radiations generated by the filament is providedon the exterior of the envelope to effect the required increase in the.bulb wall temperature without deleteriously decreasing the light outputof the lamp. The base temperature is maintained within safe limits byisolating one end of the envelope from the filament to provide arelatively cool basal end portion and attaching the base to this endportion,

A better understanding of the invention will be obtained by referring tothe accompanying drawing wherein:

FIG. 1 is an elevational view of a lamp which embodies this invention, aportion of the envelope being broken away to show the interior of thelamp in greater detail;

FIG. 2 is a perspective view of the filament mount employed in the lampshown in FIG. 1; and

FIG. 3 is an elevational view, partly in section, of an alternative lampembodiment.

With particular reference now to the drawing, in FIG. 1 there is shown alamp 10 that comprises a light-transmitting envelope 11 of globularconfiguration that has a filament 16 sealed therein. The envelope has abody portion 12 of generally spherical configuration and a basal endportion 14 of generally cylindrical configuration to which suit-ableterminal means such as a base 3 2 is secured. The diameter of the basalend portion is considerably smaller than the aforesaid body portion, asshown. The filament 16 comprises a linear coil of tungsten wire that issupported within the spherical body portion 12 of the envelope by a pairof rigid inner lead wires 17 hermetically sealed through a vitreouscircular partition 26. The partition, in turn, hermetically seals offthe body portion from the basal end portion thereby dividing theenvelope into two separate chambers A and B that are defined by theaforesaid body portion and basal end portion, respectively. The filament16 is centrally located Within chamber A, preferably symmetrical aboutthe geometrical center of the bulbous portion 12. The inner lead wires17 comprise part of a filament mount 20 that is sealed to the basal endportion 14.

As shown more particularly in FIG. 2, the filament mount 20 comprisesthe usual flare tube 22 one end whereof is sealed around the end of theinner lead wires 17 to form a press 24. The circular partition 26 isresiliently coupled to the flare tube 22 by means of the inner leadwires 17 which are hermetically .sealed through the partition, To avoidstrains the partition is preferably fabricated from a hard glass such asN-onex (Corning 7740) the coefiicient of expansion whereof matches thatof the inner leads. The ends of the inner lead wires 17 within chamber Aare suitably bent and clamped to the ends of the filament 16 to hold thelatter in substantial alignment with the axis of the mount. A supportwire 18 embedded in the partition 26 may be provided to prevent theexcessive movement of the filament in a lateral direction. The mount 20also includes the usual exhaust tube 28 which extends from the oppositeend of the flare tube 22 and communicates with an aperture 30 locatednear the press 24. A pair of outer lead wires 29 are also provided atthis end of the mount and are joined to the inner leads :17 within thestem press 24.

Fabrication of the lamp It} in accordance with this invention isachieved by sealing the rim of the flare tube 22 to the basal endportion 14 of the envelope 11 in the usual manner and concurrentlysealing the intermediate portion of the envelope to the circularpartition 26, thereby forming the aforementioned chambers A and B. Asshown in FIG. 1, chamber A contains the tungsten filament 16, thesupport wire 18 and the innermost ends of the inner lead wires 17,whereas chamber B contains the remainder of the inner leads and theflare tube 22. Chamber A is evacuated and a predetermined quantity ofiodine vapor, such as 0.25 micromole per cc. of chamber volume, is fedtherein through a glass tubulation attached to the bowl end of the bodyportion 12, which tubulation is then sealed off leaving a protruding tip34 as shown. Chamber B is evacuated through the exhaust tube 28 which isthen sealed off in the usual manner. The base 32 is then attached to thebasal end portion 14 and the outer leads 29 are connected to the baseterminals in the regular manner to complete the lamp. Since the basalend portion 14 is isolated or partitioned off from the filament 16, itwill operate at a much lower temperature than the body portion 12 andthereby maintain the base temperature of the lamp 110 within safelimits. If desired, the chamber B can be filled with nitrogen to provideincreased cooling of the basal end portion 14 and to minimize the dangerof arcing therein In order to retard the vaporization of the filament 16as much as possible and prevent the possibility of arcing, chamber A inaddition to iodine vapor also desirably contains a filling of inert gas,such as argon, krypton, xenon or nitrogen or a mixture thereof at apressure of about 500 mm. of mercury for example. The inner leads 1'7and support wire 18 are also fabricated from a refractory metal, such astungsten, molybdenum or platinum for example, that is not deleteriouslycorroded by the iodine. If molybdenum is used, an overwinding oftungsten wire can be used to cool the leads and prevent the undesirableformation of molybdenum iodide as disclosed in the aforesaid Fridrich etal. patent. The outer leads 29 located within the basal end portion 14can be fabricated from the usual material such as nickel ornickel-plated iron or the like.

The wattage rating of the filament 16 is such that it operates at atemperature above 1400 C., which temperature is required to effect thedissociation of the tungsten iodide into tungsten and iodine vapor andthus sustain the desired tungsten gettering cycle described in theaforementioned patent to Fridrich et al. However, in contrast to thevery small bulbs used in the prior art designs the size of the sphericalbody portion 12 compared to the size and rating of the filament 16 issuch that the inner wall surfaces of the body portion, or at least apart thereof, are too remote from the filament to attain a minimumnormal operating temperature of about 250 C. necessary to trigger thedesired iodine-tungsten reaction. That is to say, the bulb size isconsiderably larger than would normally be used in a conventionaliodine-cycle lamp. The resultant deficiency in bulb wall temperature isovercome in accordance with this invention by providing a thinheatconserving light-transmitting coating 13 on the spherical bodyportion 12 of the envelope 11. As shown in FIG. 1, this coating ispreferably located on the outer surface of the body portion 12 andterminates at the necked-in region where the partition 26 is joined tothe envelope.

Any material that reflects infrared radiations but transmits visibleradiations generated by the filament 16 and which will withstand therelatively high temperatures involved can be used as the coating 13, asfor example, a substantially transparent optically thin iridescent layercomprised essentially of tin oxide or titanium dioxide. It has beenfound that the bulb wall temperature of a given lamp is surprisinglyincreased by about 100 C. when an exterior coating of tin oxide, such asthe so-called EC coating marketed by the Corning Glass Works, is appliedto the envelope. Coatings of this character will transmit up to about90% of the visible radiations generated by the filament and transmittedby the envelope.

The increase in bulb wall temperature effected by the heat-conservinglight-transmitting coating 13 permits the use of filaments of lowerwattage rating or, conversely, larger size bulbs than was heretoforepossible in such iodine-containing lamps. Thus, in contrast to thepractice heretofore, envelopes having a minimum dimension greater thanabout 1 /2 inches can be employed with filaments of a rating as low aswatts thereby permitting the use of more practical bulb sizes andconfigurations.

In order to insure that the surface of the partition 26 that facestowards the filament 16 also operates at a sufiiciently hightemperature, the opposite face thereof, that is, the one disposed towardthe base 32, is desirably coated with a layer 27 of infrared reflectingmaterial, preferably one which also reflects visible radiations, as forexample a layer of aluminum or the like. A coating of this characterwill not only serve to further reduce the temperature within chamber B,and thus the base temperature of the lamp, but will reflect back intothe chamber A and out of the lamp li ht rays that would otherwise belost in the basal end portion 14. Of course, if the reflective coating27 is electrically conductive an area free from coating must be providedaround at least one of the outer lead wires 29 to prevent a shortcircuit.

In order to minimize the possibility of breakage due to thermal shock,the envelope 11, flare tube 22 and partition 26 are preferablyfabricated from a suitable thermally shock-resistant glass, such asNonex or the like, or from quartz.

The following specific examples will illustrate the wide selection ofwattage ratings and bulb sizes afforded by this invention. If thefilament 16 employed in the lamp 10 shown in FIG. 1 has a wattage ratingof 100 watts at volts and a length of about 1", the diameter of thespherical body portion 12 would be approximately 2" and that of thebasal end portion 14 approximately 1%". A tungsten filament of this sizeand rating operates at a temperature of about 2500 C. and is thereforesusceptible to erosion by progressive evaporation. It should also benoted that this temperature is considerably higher than the minimumfilament temperature of about 1400" C. necessary to effect thedecomposition of the tungsten iodide into tungsten and iodine vapor. Theoverall lamp length in this case would be about 4 the same as that of astandard 100 watt A19 general lighting lamp. Since the 2" (or so-calledG16) bulb used in this particular embodiment is smaller than the A19bulb normally used with this wattage filament, the higher bulb walltemperature produced by this reduction in bulb size plus the increaseeffected by the heat-conserving coating 13 will provide the minimum bulbwall temperature of about 250 C. required for the iodine-tungstenreaction. The base 32 in this case would be a conventional medium screwtype employed on ordinary general lighting lamps of this size.

General lighting lamps of higher wattage rating can also be provided byproportionately increasing the size of the filament and envelope. Forexample, by employing a coiled filament 16 that has a rating of 1000Watts at 120 volts, and increasing the maximum diameter of the envelope11 to approximately 5" (a G40 type bulb), a high-efficiencyiodine-containing general lighting lamp suitable for industrial oroflice lighting and the like can be provided. The base 32 in this casewould be of the mogul type conventionally employed on general lightinglamps of this size.

This invention is not limited to lamps having globularshaped envelopes.The same advantageous results can, for example, also be achieved byusing an envelope 11a of generally cylindrical configuration thereby toprovide a tubular-shaped lamp 10a such as that shown in FIG. 3. In thiscase, both the body portion 12a and basal end portion 14a of theenvelope 11a are of generally cylindrical configuration and the coiledtungsten filament 16a is proportionately lengthened and positioned toextend along and be substantially coincident with the envelope axis. Oneof the inner lead wires 17a is lengthened to accommodate the longerfilament, as shown. The envelope 11a is also divided into two separatechambers A and B by a partition 26a, and a heat-conservinglighttransmitting coating 13a is provided on the body portion 12a of theenvelope in the same manner as described above in connection with theglobular-shaped lamp 10. A support 18a may also be provided to preventthe filament from sagging or to restrict its lateral movement, and areflective coating 27a may be provided on one side of the partition 26ato further reduce the base temperature.

As a specific example of a suitable correlation of design parameters fora tubular-shaped lamp of the aforesaid construction, the filament 16amay have a rating of 100 watts at 120 volts and have a length ofapproximately 1 /2". The outside diameter of the envelope 11a in thiscase would be approximately 1%" (a T type bulb), the length of chamber Aapproximately 2" and the overall lamp length approximately 4 The base32a would be of the medium screw type generally used for this sizegeneral lighting lamp.

As will be appreciated from the foregoing, the desired objects of theinvention have been achieved by providing an iodine-containing lamp thatnot only exhibits the improved efficiency and life effected by thegettering action of the iodine, but which can be made in a variety ofwattage and bulb-sizecombinations heretofore not available or practical.Moreover, a lamp of this type has been provided which can be used forgeneral lighting purposes and be safely operated in existing sockets andfixtures.

While several embodiments have been shown and described in detail, itwill be appreciated that various modifications in the configuration andorganization of parts can be made without departing from the spirit andscope of this invention.

I claim:

1. An electric incandescent lamp comprising, a lighttransmittingvitreous envelope, a tungsten filament sealed within said envelope andhaving a predetermined rated voltage, said filament when lighted at saidrated voltage having an operating temperature above 1400 C. and beingsuceptible at such temperature to erosion by vaporization of tungstenonto the walls of said envelope with resultant blackening thereof, aquantity of iodine in said envelope sufficient to combine chemicallywith said vaporized tungsten at a temperature between about 250 to 1200C. and sustain a regenerative gettering cycle that redeposits suchvaporized tungsten on said filament, lead wires sealed through saidenvelope and connected to and supporting said filament, the enclosedportions of said lead wires being fabricated from a metal that issubstantially resistant to the corrosive action of said iodine, thedimensions and spatial relationship of said envelope relative to saidfilament being such that part of the filament-enclosing portion of saidenvelope is heated to a temperature below 250 C. when the filament isoperated at its rated voltage, and light-transmitting means on thefilament-enclosing portion of said envelope for conserving heatgenerated by said filament and maintaining the operating temperature ofthe inner surface of said envelope portion above 250 C. when the lamp isoperated at said rated voltage.

2. An electric incandescent lamp as set forth in claim 1 wherein saidlight-transmitting heat-conserving means comprises a thin coating ofinfrared-reflecting material selected from the group consisting of tinoxide and titaniurn dioxide.

3. An electric incandescent lamp as set forth in claim 1 wherein saidlight-transmitting heat-conserving means comprises a thin layer of tinoxide on the outer surface of said envelope.

4. An electric incandescent lamp as set forth in claim 1 wherein saidlight-transmitting heat-conserving means comprises a thin layer oftitanium dioxide on the outer surface of said envelope.

5. An electric incandescent lamp comprising; an envelope having a basalend portion and a light-transmitting body portion that are hermeticallysealed off from one another by a partition and evacuated; a coiledtungsten filament sealed within and located substantially centrally ofsaid body portion; said filament having a predetermined rated voltageand, when lighted at such voltage, having an operating temperature above1400 C. and being susceptible at such temperature to progressivevaporization whereby tungsten particles are deposited on the inner wallsurfaces of said body portion with attendant blackening thereof; aquantity of iodine in said body portion sulficient to combine chemicallywith said deposited tungsten particles at a temperature between about250 to 1200 C. and sustain a regenerative gettering cycle thatredeposits the vaporized tungsten on said filament; terminal meanssecured to said basal end portion; lead wires extending through saidbasal end portion and sealed through the partition between said basalend and body portions and connecting said filament with said terminalmeans; the portions of said lead wires within said body portion beingfabricated from a refractory metal selected from the group consisting oftungsten, molybdenum and platinum and comprising sup ports for saidfilament; the dimensions and spatial relationship of the body portion ofsaid envelope relative to said filament being such that said bodyportion is heated to a temperature below 250 C. when the filament isoperated at its rated voltage; and light-transmitting means on the bodyportion of said envelope for conserving heat generated by said filamentand maintaining the operating temperature of the inner surface of saidbody portion above 250 C. when the lamp is operated at the aforesaidrated voltage.

6. An electric incandescent lamp as set forth in claim 5 wherein; theminimum dimension of the body portion of said envelope is greater thanabout one and a'half inches, and said light-transmitting heat-conservingmeans comprises an infrared-reflecting coating on the outer surface ofsaid body portion.

7. An electric incandescent lamp as set forth in claim 5 wherein, thebody portion of said envelope is of generally spherical configuration,and said filament is substantially symmetrical about the geometricalcenter of said body portion.

8. An electric incandescent lamp as set forth in claim 5 wherein; thebody portion of said envelope is of generally spherical configuration,the basal end portion of said envelope is of generally cylindricalconfiguration and has a diameter considerably smaller than the diameterof said body portion, and said filament is of generally linearconfiguration and extends along the axis of said envelope.

9. An electric incandescent lamp as set forth in claim 5 wherein thebody portion of said envelope also con tains a filling of inert gas, andthe basal end portion contains a filling of nitrogen.

10. An electric incandescent lamp as set forth in claim 5 wherein, saidenvelope is of generally cylindrical configuration, and said filament isof linear configuration and substantially aligned with the axis of saidenvelope.

11. An electric incandescent lamp as set forth in claim 5 wherein thepartition between the body and basal end portions of said envelope iscoated with infrared-reflecting material.

12. An electric incandescent lamp as set forth in claim 5 wherein thepartition between the body and basal end portions of said envelope iscoated with material that reflects both infrared and visible radiations.

13. An electric incandescent lamp having a predetermined rated voltageand comprising, in combination, a sealed light-transmitting envelopecontaining a filling of inert gas and from about .01 to 1 micromole ofiodine per cubic centimeter of envelope volume, a tungsten filamentsupported within said envelope and adapted when lighted at said ratedvoltage to attain an operating temperature above 1400 C. and heat theinner surface of said envelope to a temperature below 250 C., andlighttransmitting means on at least a portion of said envelope forconserving heat generated by said filament and maintaining the operatingtemperature of the inner surface of said envelope above 250 C.

14. An electric incandescent lamp as set forth in claim 13 wherein saidlight-transmitting heat-conserving means comprises a thin coating ofinfrared-reflecting material.

15. An electric incandescent lamp having a predetermined rated voltageand comprising, in combination, a sealed light-transmitting envelopehaving a substantially spherical body portion approximately two inchesin diameter and a generally cylindrical end portion of smaller diameter,a filling of inert gas and a predetermined amount of iodine within saidenvelope, a pair of lead wires sealed through said envelope and havingiodineresistant end portions that extend into the spherical body portionthereof, a coiled tungsten filament having a rating of approximately 100watts at said rated voltage and a length of approximately one inchconnected to the inner end portions of said lead wires and supportedthereby in centrally located position within the spherical body portionof said envelope, means for maintaining the operating temperature of thecylindrical end portion of said envelope below that of said sphericalportion, terminal means secured to the cylindrical end portion of saidenvelope and connected to said lead wires, and a coating oflight-transmitting infrared-reflecting material on the outer surface ofthe spherical body portion of said envelope that conserves a sufiicientamount of the heat generated by said filament to maintain the innersurface of the spherical portion of said envelope at a temperature above250 C. when the lamp is operated at its rated voltage.

16. An electric incandescent lamp having a predetermined rated voltageand comprising, in combination, a sealed light-transmitting envelope oftubular configuration that is approximately 1% inches in diameter anddefines an elongated chamber approximately two inches in length, afilling of inert gas and a predetermined amount of iodine within saidenvelope, a pair of lead wires sealed through one end of said envelopeand having inwardly extending iodine-resistant end portions, a coiledtungsten filament having a rating of approximately watts at said ratedvoltage and a length of approximately 1% inches connected to the innerend portions of said lead wires and supported thereby in said chamber insubstantially coaxial relationship with said envelope, terminal meanssecured to the sealed end of said envelope and connected to said leadwires, and a coating of lighttransmitting infrared-reflecting materialon the outer surface of said envelope that conserves a sufficient amountof the heat generated by said filament to maintain the inner surface ofthe portion of said envelope that defines said chamber at a temperatureabove 250 C. when the lamp is operated at its rated voltage.

References Cited by the Examiner UNITED STATES PATENTS 1,425,967 8/22Hoffman 313-112 1,994,056 3/35 Trompeter 313-222 X 2,103,028 12/37 Bol313-43 X 2,142,104 l/39 Birdseye 313-43 X 2,859,369 11/58 Williams eta1. 313- X 2,879,449 3/59 Macksoud 313-113 X 2,883,571 4/59 Fridrich etall 313-222 X DAVID J. GALVIN, Primary Examiner.

ARTHUR GAUSS, JAMES D. KALLAM, Examiner's.

13. AN ELECTRIC INCANDESCNET LAMP HAVING A PREDETERMINED RATED VOLTAGEAND COMPRISING, IN COMBINATION, A SEALED LIGHT-TRANSMITTING ENVELOPECONTAINING A FILLING OF INERT GAS AND FROM ABOUT .01 TO 1 MICROMOLE OFIODINE PER CUBIC CENTIMETER OF ENVELOPE VOLUME, A TUNGSTEN FILAMENTSUPPORTED WITHIN SAID ENVELOPE AND ADAPTED WHEN LIGHTED AT SAID RATEDVOLTAGE TO ATTAIN AN OPERATING TEMPERATURE ABOVE 1400*C. AND HEAT THEINNER SURFACE OF SAID ENVELOPE TO A TEMPERATURE BELOW 250*C., ANDLIGHTTRANSMITTING MEANS ON AT LEAST A PORTION OF SAID ENVELOPE FORCONSERVING HEAT GENERATED BY SAID FILAMENT AND MAINTAINING THE OPERATINGTEMPERATURE OF THE INNER SURFACE OF SAID ENVELOPE ABOVE 250*C.